The present invention relates to a process for preparing cyclopentadienyl compounds. More particularly, it relates to a process for preparing alkylidene-bridged bis-cyclopentadienyl compounds. The invention also relates to a class of compounds obtainable from this process.
Compounds having two cyclopentadienyl rings joined by a structural bridge are known and broadly used in the synthesis of organometallic compounds, mainly for the preparation of ansa-metallocenes which are active as catalyst components in the polymerization of olefins.
From the European application EP 129.368 are known metallocene compounds comprising cyclopentadienyl rings linked each other by a bridge constituted by an alkylene group having 1 to 4 carbon atoms. However, in said application the preparation of such compounds is not disclosed.
The European application EP 416.566 discloses propylene polymer having low molecular weight prepared by bulk polymerization carried out in the presence of a catalyst comprising (A) an alumoxane and (B) a metallocene compound in which the cyclopentadienyl rings, equal or different, are linked with a bridge having formula xe2x80x94R5CR6xe2x80x94 wherein R5 and R6 can have different meanings. The ligands of the metallocene compounds are prepared by reacting a cyclopentadienyl compound, previously treated with an organo lithium compound, with a fulvene compound. If the fulvene is corresponding to the cyclopentadienyl compound, symmetric ligand can be obtained. Nevertheless, this method gives unsatisfactory yields and requires, also for the preparation of symmetric ligands, a previous step in which the fulvene is prepared and separated with consequent lowering of the whole reaction yield.
Isopropylidene-bridged cyclopentadienyl compounds have been prepared by I. E. Nifant""ev et al. in J.Chem. Research 1992, 162 by reacting a substituted cyclopentadienyl compound with 6,6-dimethylfulvene in the presence of a NaOH THF system. Also in this case the 6,6-dimethylfulvene is separately prepared. Furthermore, since the 6,6-dimethylfulvenes having substituents on the cyclopentadienyl ring do not react in these conditions it is impossible to obtain isopropylidene-bridged bis-cyclopentadienyl compounds having substituents on the cyclopentadienyl ring.
According to the same author in Organometallics 1991, 10, 3739, isopropylidene-bis(cyclopentadiene) is prepared by only one step reacting cyclopentadiene and acetone in the presence of the system NaOH THF. The yields obtained are about 60%. However, in these conditions substituted cyclopentadienes do not react with acetone.
I. F. Urazowski et al. at the Xth Fechem Conference on Organometallic Chemistry held on Sep. 5-10, 1993 in Agia Pelagia, Cretexe2x80x94Greece, presented metallocene complexes of Ti and Zr obtained from two dicyclopentadienyl-dimethyl-methanes, namely those having an isopropyl or tertbutyl substituent on the 3-position of each cyclopentadienyl ring. However, only mechanisms of the formation of those complexes and their structural features on the basis of X-ray analysis were discussed, whilst the preparation of the corresponding dicyclopentadienyl-dimethyl-methanes was not described.
Therefore, it would be highly desirable to provide an easy and advantageous route to the preparation of the general class of bis-cyclopentadienyl compounds bridged by a single carbon atom.
The applicant has now surprisingly found that, by operating under particular conditions, alkylidene-bridged bis-cyclopentadienyl compounds having substituents on the cyclopentadienyl rings can be prepared by means of an easy one-step process.
Therefore, it is an object of the present invention a process for preparing symmetric bridged bis-cyclopentadienyl compounds having the general formula (I): 
wherein the double bonds of the cyclopentadienyl ring can be in any of the allowed positions wherein R1, R2, R3 and R4, which can be identical or different, are hydrogen atoms or C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals which can contain atoms of Si or Ge, and furthermore two adjacent R1, R2, R3 and R4 substituents on the same cyclopentadienyl ring can form a ring having 5 to 8 carbon atoms;
R5 is a hydrogen atom or a xe2x80x94CHR7R8 group;
R6 is a C6-C20-aryl radical or a xe2x80x94CHR9R10 group;
R7, R8, R9 and R10, which can be identical or different, are hydrogen atoms or C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals which can contain hetero atoms such as nitrogen, phosphorus, oxygen or sulphur, or two R7, R8, R9 and R10 substituents can form a ring having 3 to 8 carbon atoms, which can also contain hetero atoms;
said process comprising the reaction of a carbonyl compound of formula (II): 
wherein R5 and R6 have the meaning given above, with a cyclopentadienyl compound of formula (III): 
wherein the double bonds in the cyclopentadienyl rings can be in any of the allowed positions wherein R1, R2, R3 and R4 have the meaning given above, said reaction being carried out in the presence of a base and of an oxygen-containing solvent having an atomic ratio carbon/oxygen not higher than 3.
The double bonds of the cyclopentadienyl rings in the compounds of formula (I) and (III) can be in any of the allowed positions.
The choice of the solvent is critical for the invention. Unsuitable solvents will not give the desired final product, or will give it with unsatisfactory yields.
A particularly suitable class of solvents for use in the process of the invention are the polyethers such as, for example:
diethers, such as dimethoxyethane, diethoxyethane,
triethers, such as diglyme,
crown ethers,
mono-, di-, oligo- or polyethyleneglycole.
Examples of bases suitable for use in the process of the present invention are, for instance, the alkali or alkali earth metal hydroxides, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide. Potassium hydroxide is the preferred.
According to a particularly preferred embodiment, the process of the invention is carried out in the presence of the system consisting of potassium hydroxide and dimethoxyethane.
The reaction temperature is generally comprised between xe2x88x9250xc2x0 C. and the boiling temperature of the solvent.
The time of the reaction can vary in a wide range. Generally it is comprised between 2 minutes and 24 hours, more typically between 30 minutes and 4 hours.
In the above reaction, the molar ratio of the cyclopentadienyl compound (III) to the carbonyl compound (II) can vary in a very wide range and, in dependence of said (III)/(II) molar ratio, different embodiments can be practised which permit to obtain the desired final products. Each of said embodiments permits to obtain a different type of final products. However, the above molar ratio is generally equal to or lower than 2.
According to a preferred embodiments of the process of the invention, the reaction between the cyclopentadienyl compound (III) and the carbonyl compound (II) is conducted with a molar ratio (III)/(II) of about 2:1. When such a ratio is used, in dependence of the choice of the type and the number of the substituents in the formulae (II) and (III), different alkylidene-bridged bis-cyclopentadienyl compounds can be prepared in a single step.
Accordingly, starting from cyclopentadienyl compounds of formula (III) in which at least one of the R1, R2, R3 and R4 substituents is a C1-C10 alkyl group, compounds belonging to the class of the alkylidene-bridged bis(alkyl-substituted-cyclopentadienyl) compounds can be obtained, in yields generally higher than those of the processes of the prior art.
In particular when, operating at a (III)/(II) molar ratio of about 2:1, acetone is employed as the carbonyl compound of formula (II) and an alkyl-substituted cyclopentadienyl compound as the compound of formula (III), bridged bis-alkyl-substituted-cyclopentadienes of formula (IV):
2,2-bis(CpRxe2x80x2nH4xe2x88x92n)propanexe2x80x83xe2x80x83(IV)
in which Rxe2x80x2 is a C1-C10 alkyl radical like methyl, ethyl, isopropyl, t-butyl and the like, and n is an integer comprised between 1 and 4, can be obtained in a single step with yields higher than 75%. In the case of 2,2-bis(monoalkyl-cyclopentadienyl)propanes, the NMR spectra show that the alkyl substituents are connected with the xcex2-carbon atom of the cyclopentadienyl ring. Examples of compounds of formula (IV) are:
2,2-bis(3-methyl-cyclopentadienyl)propane,
2,2-bis(3-ethyl-cyclopentadienyl)propane,
2,2-bis(3-isopropyl-cyclopentadienyl)propane,
2,2-bis(3-t-butyl-cyclopentadienyl)propane,
2,2-bis(2,4-diethyl-cyclopentadienyl)propane,
2,2-bis(2-methyl-4-isopropyl-cyclopentadienyl)propane,
2,2-bis(2-methyl-4-t-butyl-cyclopentadienyl)propane,
2,2-bis(2,3,4,5-tetramethyl-cyclopentadienyl)propane,
2,2-bis(2,3,4,5-tetraethyl-cyclopentadienyl)propane.
Another class of compounds which is possible to obtain in a single step, operating at a (III)/(II) molar ratio of about 2:1 is that of alkylidene-bridged bis-indenyl compounds. These compounds are obtainable by starting from compounds of formula (III) in which the R1 and R2 substituents or the R3 and R4 substituents form a benzene ring, that is indenyls or substituted indenyl compounds.
In this class of alkylidene-bridged bis-indenyl compounds, particularly preferred are the 2,2-bis(indenyl)propanes which can be obtained by reacting indenyl compounds with acetone in the presence of a suitable alkali/solvent system such as KOH/DME. Examples of such compounds are:
2,2-bis(indenyl)propane,
2,2-bis(3-methyl-indenyl)propane,
2,2-bis(3-ethyl-indenyl)propane,
2,2-bis(3-isopropyl-indenyl)propane,
2,2-bis(3-t-butyl-indenyl)propane,
2,2-bis(4,7-dimethyl-indenyl)propane.
Moreover, substituted bridged bis-indenyl compounds can be prepared by a post-treatment of the 2,2-bis(indenyl)propane obtained according to the above embodiment. For example, 2,2-bis(3-trimethylsilyl-indenyl)propane can be obtained by treating the dilithium salt of 2,2-bis(indenyl)propane with trimethylchlorosilane.
Examples of bis-cyclopentadienyl compounds bridged with a group other that isopropylidene, obtainable with the process of the invention are:
1,1-bis(cyclopentadienyl)cyclopentane,
1,1-bis((1H)inden-3-yl)cyclopentane,
1,1-bis(cyclopentadienyl)cyclohexane,
1,-bis((1H)inden-3-yl)cyclohexane,
1,1-bis(cyclopentadienyl)cycloheptane,
1,1-bis((1H)inden-3-yl)cycloheptane,
1,1-bis(cyclopentadienyl)cyclopropylethane,
1,1-bis((1H)inden-3-yl)cyclopropylethane,
bis(cyclopentadienyl)phenylmethane,
bis(indenyl)phenylmethane,
4,4-bis-cyclopentadienyl-1-methyl-piperidine.
4,4-bis-indenyl-1-methyl-piperidine.
According to another embodiment of the invention, the carbonyl compound of formula (II) can be used in excess with respect to the stoichiometric molar ratio (III)/(II) of 2:1. In particular, the molar ratio (III)/1(II) can be of about 2:3.
In such conditions, cyclopentadienyl compounds of formula (I) having alkylidene substituents in the xcex2-position on the cyclopentadienyl ring can be obtained as main products of the reaction.
If the carbonyl compound of formula (II) is employed in great excess, it can be used as the reaction solvent.
Therefore, it is another object of the present invention a process for preparing bridged cyclopentadienyl compounds having the general formula (VI): 
wherein R1, R3, R4, R5, and R6 have the meaning given above, and the R2 substituents, which can be identical or different, are alkylidene radicals of formula (V): 
wherein R5 and R6 have the meaning given above, said process comprising the reaction of a carbonyl compound of formula (II): 
wherein R5 and R6 have the meaning given above, with a cyclopentadienyl compound of formula (III):
as reported above
wherein R1, R2, R3 and R4 have the meaning given above, in a molar ratio (II)/(III) equal or higher than 1.5, said reaction being carried out in the presence of a base.
For example, when the reaction between indene and acetone is carried out with molar ratio indene:acetone of about 2:3, or with an excess of acetone employing acetone as reaction solvent, the compound obtained is 2,2-bis(3-benzo-6,6-dimethyl-fulvene)propane. This is a very versatile compound which can be transformed, according to well known reaction, in various 2,2-bis(indenyl)propanes with substituents in the 3-position of the indenyl groups.
For example, 2,2-bis(3-benzo-6,6-dimethyl-fulvene)propane can be reacted in a suitable solvent with hydrides, such as LiH or LiAlH4, or metallorganic compound, such as LiMe, to obtain respectively 2,2-bis(3-isopropyl-indenyl)propane or 2,2-bis(3-t-butyl-indenyl)propane directly in the anionic form to be in turn converted in the metallocene compound.
The bridged cyclopentadienyl compounds obtained from the reaction between the carbonyl compound of formula (II) and the cyclopentadienyl compound of formula (III) according to the present invention, are recovered and separated from the reaction mixture by the known technique such as extraction, crystallization, distillation, chromatography etc.
The alkylidene-bridged bis-cyclopentadienyl compounds obtainable by the process of the present invention can be employed to prepare the corresponding metallocene compounds with transition metals such as titanium, zirconium of hafnium, which are useful as catalytic components in the polymerization of olefins.
Some of the alkylidene-bridged bis-cyclopentadienyl compounds obtainable with the process of the present invention are not known at the date of the present invention. Therefore, it is a further object of the present invention a bridged cyclopentadienyl compound having the general formula (I): 
wherein the double bonds of the cyclopentadienyl rings can be in any of the allowed positions, wherein R1, R2, R3, R4, R5 and R6 are defined as above, with the proviso that, when the R5 and the R6 substituents are methyl groups, the following conditions apply:
at least one of the R1, R2, R3 and R4 substituents is different from a hydrogen atom,
if the R1, R2 and R4 substituents are hydrogen atoms, the R3 substituents are other than isopropropyl or tertbutyl groups, and
the two bridged ligands are other than unsubstituted indenyls.
Particularly interesting new bis-cyclopentadienyl compounds of formula (I) obtainable from the process of the invention are those in which the R3 substituents are carbon, silicon or germanium atoms substituted with three alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl groups having 1 to 10 carbon atoms, and wherein the R4 substituents are hydrogen atoms. Examples of such compounds are:
2,2-bis(3-t-butyl-cyclopentadienyl)propane,
2,2-bis(2-methyl-4-t-butyl-cyclopentadienyl)propane,
2,2-bis(3-t-butyl-indenyl)propane,
2,2-bis(3-trimethylsilyl-indenyl)propane.